The instant invention relates to a circuit breaker of the puffer type, and more particularly, to a puffer breaker having a nozzle designed to maximize arc cooling by a high speed flow of insulating gas therethrough.
During circuit interruption by a puffer breaker, an arc is drawn between the breaker contacts. The arc is cooled by adiabatic compression of insulating gas in a puffer assembly during breaker opening, as the insulating gas is blown over the arc to cool the arc. In puffer breakers employing a slowly expanding nozzle of insulating material, application to high current circuit interruption results in excessive ablation of the nozzle material, which clogs the nozzle throat, and blocking of the insulating gas flow by the movable electrode passing through the nozzle throat of the type having small expansion angle. These results increase the time required for deblocking the circuit breaker nozzle, when the arc current approaches zero, thereby increasing the circuit interruption time lapse.
One prior art approach to improving interruption characteristics has been to provide a downstream electrode substantially smaller than the nozzle throat diameter. Such a configuration allows a significant portion of the insulating gas to escape through the nozzle throat prior to current zero, resulting in a lower gas pressure and reduced arc interruption capability of the insulating gas at the critical moment of current zero.
An alternative approach to overcoming the problem of ablation is to employ a very short downstream nozzle section having the characteristics of essentially an orifice. Such a construction reduces the nozzle ablation and blocking of the flow by the moving electrode, but diminishes the thermal interruption performance of the insulating gas flowing over the arc downstream of the nozzle throat, since it does not confine the flow downstream of the nozzle throat.